1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display, a plasma display, a DMD display, an electrochromic display or an electron emission element array, and more particularly to the connection method for the reference potential wiring for the drive means for such display.
2. Related Background Art
For facilitating the understanding of the difference between the present invention and the conventional configuration, there will at first be explained, as an example, a liquid crystal display device.
There have conventionally been proposed various apparatus equipped with the liquid crystal display device, of which an example is illustrated in FIG. 1.
As is already known, a liquid crystal display P is provided with a pair of substrates arranged in mutually opposed manner, between which ferroelectric liquid crystal is injected. On the substrates there are respectively formed a plurality of stripe-shaped common electrodes 1 (first electrode group) and a plurality of stripe-shaped segment electrodes 2 (second electrode group), the electrodes constituting a matrix electrode array.
These common electrodes 1 are connected to common drive circuits (first drive means or first drive circuits) 3, which are in turn connected to a bus board (first drive means or first bus board) 7. The bus board 7 is connected to a control board (control means) 9 through two cables 7A, 7B of which the cable 7A serves to provide the common drive circuits 3 with power supply voltages V1, VC, V2 as reference voltages. In response to the supply of the power supply voltage V1, the common drive circuits 3 suitably apply a common signal of a predetermined wave form to the common electrodes 1. A power supply voltage and control signals for driving the common drive circuits 3 are supplied through the other cable 7B.
On both sides of the liquid crystal display device P there are respectively provided segment drive circuits (second drive means or second drive circuits) 5, 6 to which the segment electrodes 2 are alternately connected, as partly illustrated in FIG. 1. These segment drive circuits 5, 6 are respectively connected to bus boards (second drive means or second bus boards) 10, 11, which are in turn connected to the control board 9 respectively through two cables 10A, 10B and 11A, 11B. The cables 10A, 11A serve to provide the segment drive circuits 5, 6 with power supply voltages V3, VC, V4. In response to the supply of the power supply voltage V3, the drive circuits 5, 6 apply a segment signal of a predetermined wave form to the segment electrodes 2. A power supply voltage and drive signals for driving the segment drive circuits 5, 6 are supplied the other cables 10B, 11B. The liquid crystal display device P is driven by the signal application by these electrodes 1, 2.
The conventional device has been associated with a drawback that a steeply varying current generated at the switching of liquid crystal flows into the power supply lines for the liquid crystal, thereby causing, by electromagnetic induction, a variation for example in the reference ground potential. Such variation becomes particularly large in the display of certain specified patterns, thus eventually inducing an erroneous function of the drive circuits. For resolving such variation in the ground potential, the present inventors have investigated a method of connecting the ground of the bus boards with a metal casing, but such method has been identified as difficult to adopt because of the structure of the device.